It's a common phrase said usually to keep from revealing the actual meaning to the person who in fact is an lotl.

Lotl:
One(s), such as people, that seemingly came out of the ordinary. They develop a strong aura of unrequited love to the same gender, only being noticed by those who are similar in hiding.

These lotls are not necessarily inappropriate, but instead full of love for each other. "On the loose" is a phrase that catches the actual meaning of being out and only known by the mind or possibly a gaydar.

It suggests the fact that they are indeed lesbians, but are not officially out. You can jut tell they are without even asking them.